In the poultry industry, in particular the chicken industry, automatic egg examining devices using the transparency of the egg in order to differentiate between fertilized and unfertilized eggs are known. These devices comprise emission means for emitting a light beam in the direction of an egg to be examined, receiving means for receiving the light beam passing through the egg, and means for processing data regarding the light beam received by said receiving means so as to determine the state of the egg. As a function of the level of absorption of the light beam passing through the egg, or the level of transparency of the egg, the data processing means can differentiate between fertilized eggs, i.e. eggs containing an embryo, and unfertilized eggs, including infertile eggs and rotten eggs. Some devices can also differentiate between live fertilized eggs containing a live embryo and dead fertilized eggs containing a dead embryo.
These examining devices conventionally comprise a despatch conveyor for transporting the eggs placed in their horizontal incubation racks or trays, emission means and receiving means being arranged on either side of the despatch conveyor. The emission means are generally constituted by emitters formed of light sources, such as filament lamps or light emitting diodes, conventionally of approximately 12 W, the receiving means being formed of photodiode-type receivers having receiving surface areas of approximately 0.5 mm2. In order to obtain satisfactory transparency measurements, the emitters and receivers are arranged opposite one another in the same vertical plane.
The main drawback of said vertical examination systems is their low resistance to waste originating from the egg trays. The waste, such as bits of shell or the contents of broken eggs, feathers or other organic material, fall by means of gravity onto the emitters or receivers arranged below the trays which results in measurement variations and errors. In order to limit said measurement variations and errors, it is thus necessary for the examining device to be serviced on a very regular basis. Consequently, it has been suggested, in particular in patent document FR 2 768 517, to place a protective screen between the trays and the emitters arranged below said trays. The light beams from the emitters pass through the protective screen and automatic cleaning means are associated with said protective screen. Mechanical systems of this type are bulky and of complex design.